Make sauce. In a small bowl, mix together soy sauce, hoisin sauce and sesame oil.
In a work, heat canola oil and cook garlic and onion over medium heat for about 2 minutes. Add ground turkey and cook until ground turkey is cooked through. Add both bell peppers and cook until bell peppers are tender.
Stir in the sauce and add salt and black pepper to taste. Toss to coat. Remove the work from the heat and let cool for about 15 minutes at room temperature.
Make sandwiches. Spread mayonnaise (1 teaspoon for each) on the bottom of each bun and put the red leaf lettuce (5 for each). Take the filling with slotted spoon and put on the lettuce. Put the top of each bun to close sandwich.