Preheat oven to 475°F. Coat a baking sheet with cooking spray.
Combine mustard, soy sauce and 1/2 teaspoon adobo sauce in a small bowl. Slice tofu crosswise into eight 1/2-inch-thick pieces. Pat dry with a paper towel and place on the prepared baking sheet. Using a spoon, spread half the mustard mixture on one side of the tofu. Turn the slices over and spread the remaining mixture on the other side.
Bake the tofu for 20 minutes.
Combine mayonnaise with the remaining 1/2 teaspoon adobo sauce in a small bowl. Spread the mixture on toasted bread. Divide the tofu, lettuce and tomato among 4 slices of toast and top with the remaining toast to make 4 sandwiches. Cut in half to serve.
Ingredient note: Canned chipotle peppers (smoked jalapenos) add heat and smokiness to dishes; the adobo sauce alone adds a spicy zest without extra heat. Look for small cans with other Mexican foods in large supermarkets. Once opened, chipotles will keep for up to 2 weeks in the refrigerator or 6 months in the freezer.