This trek is a great option to get your troop started in the Sierras.  

Car camp at the Vermilion Campground the first night, then hike in for ~7 miles to lower Graveyard Lake, make base camp, and then hang our for a day or two to fish and explore.  Return to the trailhead after ~3 days in the wilderness.

As with all Sierra treks, there are tons of options to choose from, but in general here is a possible itinerary.

Travel Day 

Drive to Vermilion Valley Resort (VVR) from Fresno and make camp at the Vermilion campground along Lake Edison (reserve sites on recreation.gov).  NOTE: The Vermilion campground is located next to VVR, but is not managed by VVR.  Elevation is about 7,500'.  It's good to arrive early so you can begin acclimating.

Dinner can either be a car camping feast ... or ... partake in the thru-hiking paradise feel of VVR and eat at their outdoor, rustic cafe.  VVR is a popular resupply location along the John Muir Trail (and Pacific Crest Trail).  It is common for 1-2 dozen thru-hikers to arrive in after ~4pm in the afternoon as they wash up at the coin operated showers and eat a hot cooked meal.  Often there will be a fire pit going in th evening as the thru-hikers trade stories, and it can be a lot of fun for scouts to talk with them.  Plus, the food is good too!  It's all part of the Sierra experience.

Hiking Day 1

Start hiking north towards Goddard Pass (see map).  The trail starts relatively flat, but let's be honest ... there's no such thing as flat in the Sierras.  That said, it's not nearly as steep as other Sierra routes, and has plenty of shade to rest in as you go.  Once you get to Upper Graveyard Meadows you'll wade through Cold Creek and head west "up" the trail to the Graveyard Lakes area.

There's some great, mostly flat tenting along the northeast side of the first lake, just inside tree cover.  This can be a good location to make basecamp.

Hiking Day 2 

Wake up, make a backpacker's breakfast and head out for a day hike exploration of all the lakes in the area.  The trail is easy to follow and quickly wanders above treeline for some gorgeous alpine Sierra views.  Brook trout are all over the place, so bring your fishing poles.  Catch and release (get your fishing licsense ahead of time), or bring some fish back to camp to cook up over a backpackers stove.  If everyone has the energy, climb up to Silver Fox Pass just north of Upper Graveyard Lake (the largest lake).  Take a swim too!

Hiking Day 3

Take a leisurly morning, finish exploring the area, break camp, and return back down the trail to your vehicles.  Either stay another night at Vermilion Campground (or VVR proper) ... or head on down the mountain towards Fresno.

This trek could easily be modified to add on more days.  

For example:

Consider crossing Silver Fox Pass to the north and make your way over to Peter Pande Lake.  From there, take the trail northeast towards Lake of the Lone Indian, Papoose Lake, and Chief Lake.  From there, you could either head up and over Goodale Pass back to VVR to the south ... retracing your route to your vehicles ... OR extend your trek further by heading to the John Muir Trail and hiking south over Silver Pass.  If you take the John Muir Trail route heading south, then you can reconnect to the eastern side of Lake Edison and take the VVR ferry back to the campground.  VVR opertes a ferry in the afternoon to shuttle JMT hikers to their lodgings.  Check with them before you begin your trek to make sure the ferry is running during the time you'll be returning.