Heat grill on high heat.
Very lightly brush the burgers with olive oil. Season well with salt and pepper. Grill for about 8 minutes, flipping once mid-way, until desired doneness. Place slices of cheese on each burger, close the grill lid for another 30 seconds until cheese starts to melt. Remove from the grill.
Take each burger bun and lightly butter the halves. Place, buttered side down on the grill to toast for a minute or so until lightly toasted. Remove from the grill.
While burgers are resting, heat 1 t olive oil in a medium nonstick pan. Add the garlic and spinach and sauté briefly until the spinach is wilted.
Serve cheeseburgers on the toasted, buttered buns with slices of red onion, sautéed spinach, and Cherry Chipotle Barbecue Sauce. Yield: 4 servings.