Step 1

Set garlic heads and shallots in an 8- or 9-inch pan. Bake in a 375° oven until garlic and shallots are very soft when pressed, 35 to 40 minutes. Let cool.

Step 2

Split baguette in half lengthwise.

Step 3

Cut root end off garlic and squeeze out soft pulp; discard skin. Cut root end off shallots, peel, and discard skin; chop soft interior. Mix garlic and shallots and spread onto cut sides of baguette.

Step 4

Peel, pit, and thinly slice the avocado. Lay slices over bottom baguette half and sprinkle lightly with salt and pepper.

Step 5

Arrange cucumber, tomatoes, and basil leaves on avocado. Cover with top half of baguette. With a serrated knife, carefully cut sandwich into 3 or 4 portions.