Slice 1 large red tomato into ½-inch-thick rounds. Set aside.
Slice 8 ounces fresh mozzarella into ½-inch-thick rounds. Set aside.
Slice 1 12-inch baguette in half length-wise. Place both halves of baguette on flat surface, cut-side up.
Optional: If toasting sandwich, preheat broiler on High, with oven rack positioned approximately 8 to 12 inches below heating element.
Add 2 tablespoons full-fat mayonnaise and 1 tablespoon pesto to small mixing bowl. Stir or whisk ingredients together until fully combined. Spread pesto mixture evenly onto cut-side of bottom baguette half.
Spoon 1 tablespoon high-quality olive oil evenly over cut-side of top baguette half. Be careful not to concentrate oil in one spot or bread can become soggy.
Place slices of tomato on bottom baguette half in one layer, with each slice slightly overlapping.
Place slices of mozzarella on top of tomato slices in one layer. Sprinkle salt and freshly cracked black pepper over mozzarella to taste.
Optional: Place sandwich halves cut-side up on baking sheet and place baking sheet under broiler. Broil sandwich 2 to 3 minutes or until bread is lightly toasted and mozzarella is melted slightly. Carefully remove baking sheet from beneath broiler.
Drizzle 1 tablespoon balsamic glaze over entire layer of mozzarella, then top mozzarella with 6 leaves fresh basil, placed evenly across sandwich.
Cover mozzarella and tomatoes with top half of baguette, placed cut-side down. Slice sandwich in half, creating two 6-inch sandwiches, and serve with dipping bowl of high-quality olive oil if desired.