Combine the mayonnaise and pesto in a small bowl. Preheat your grill to medium-high. Cut the bread widthwise in half. Cut each half in half lengthwise. Brush the cut sides with 1 Tbsp. of the olive oil. Grill the bread about 30 seconds per side, and then divide among 2 plates.
Brush the salmon with 1 Tbsp. olive oil; season with salt and pepper. Coat the bell pepper rings with the remaining oil. Lightly oil the bars of the grill. Grill the salmon 3 to 4 minutes per side, or until just cooked through. While the salmon cooks, grill the pepper rings until just tender, about 1 minute per side.
To serve, spread each sandwich with pesto mayonnaise, add lettuce leaf, grilled salmon and peppers.