Step 1

Arrange a rack 6 inches from the broiling element and heat the broiler to high. Meanwhile, cut 4 ounces fresh mozzarella cheese into 1/4-inch thick slices. Cut 3 campari tomatoes crosswise into 1/4-inch thick rounds, or 1 large tomato into 1/4-inch thick half-moons. Thinly slice 1/2 medium avocado.

Step 2

Split the baguette(s) lengthwise with a serrated knife. Place cut-side up on a baking sheet. Broil until lightly toasted (the middle should feel crunchy versus fluffy), 1 to 3 minutes. Transfer the bread cut-side up to a cutting board.

Step 3

Layer the mozzarella, tomatoes, and avocado on the bottom half of the bread. Sprinkle with 1/4 teaspoon kosher salt and 1/4 teaspoon black pepper. Top with 1/4 cup fresh basil leaves, tearing them in half if large.

Step 4

Brush 1 tablespoon extra-virgin olive oil and 1 teaspoon balsamic vinegar onto the top half of the bread. Close the sandwiches with the top half and gently press down so the top adheres to the bottom. Cut the baguette sandwich crosswise into 4 pieces and the demi baguette sandwiches into 2 pieces each.