Pre-heat barbecue over medium-high.
Assemble skewers with a mixture of salmon cubes, lemon slices, and bell pepper and onion pieces. Sprinkle with salt and pepper.
Spray barbecue with spray oil (don't be shy, you don't want the salmon to stick to the grill!).
Arrange the skewers on the grill, and cook with the lid down for 4 minutes.
Gently pry the skewers from the grill (the salmon may stick slightly, but should come off with a bit of teasing), and flip over. Put the lid down, and cook for another 4-6 minutes, until salmon is cooked through and flakes with a fork.
Serve immediately with pita bread and lemon wedges.