Heat olive oil and garlic in a frying pan over medium heat for 1 minute. Add tomato, bell pepper, and onion. Cook until soft, about 4 minutes. Season with salt and pepper and remove from heat.
While vegetables are cooking, toast bread slices. Spread hummus onto 1 slice. Spread vegan mayonnaise on the other and lightly season with salt and pepper.
Layer sun-dried tomatoes, lettuce, and cooked vegetables onto 1 slice and top with the remaining slice. Cut sandwich in half.
