1. Preheat the oven to 350°. Spread the pecans in a pie plate and bake for 8 minutes, or until lightly toasted. Transfer to a plate, let cool completely, then chop. In a bowl, mix the pecans with the butter. Season generously with salt.
2. Light a grill. In a large bowl, gently toss the vegetables. Spread the banana leaves on a work surface. Lay 4 pieces of bacon side by side in the center of the bottom half of each leaf. Spread the vegetables over the bacon and drizzle with olive oil. Season with salt and pepper. Fold the top half of each leaf over the vegetables, then tuck the sides underneath to seal. Tie the packs with kitchen string to secure.
3. Lightly brush the grate with vegetable oil. Grill the packs, bacon side down, over a medium-hot fire until you hear the juices bubble steadily, about 15 minutes. Transfer the packs to plates. Untie the packs, top the vegetables with the toasted pecan butter and serve.
Make Ahead: The pecan butter can be refrigerated for 2 days or frozen for 1 week. The assembled vegetable packs can be refrigerated overnight.
Notes: Whole banana leaves are available frozen at Latin markets and can be cut to the desired size. Wipe with a damp cloth before using.