To make pesto: Heat olive oil in a nonstick skillet over high heat. Add garlic and saute 3 to 5 minutes or until light brown. Remove from heat.
Place remaining ingredients, including 3 tablespoons water, in a food processor fitted with the metal blade. Process until smooth and creamy. Add additional water, if necessary, to make dip creamy. Makes about 2 cups.
To make sandwich: Steam zucchini, eggplant and yellow squash over boiling water for 3 to 5 minutes or microwave them in a microwave proof dish, covered, for 2 to 3 minutes on high power. Alternatively, vegetables may be grilled or broiled approximately 2 inches from a flame or heating element for 2 to 3 minutes total cooking time. Vegetables should be tender but al dente.
Spread 1 cup Navy Bean Pesto evenly over the cut side of the bottom of the bread loaf. Layer zucchini, yellow squash, and eggplant over pesto. Layer thinly sliced red onions and tomatoes over the cooked vegetables. Top vegetables with the spinach leaves. Spread remaining 1 cup Navy Bean Pesto on the cut side of the top of the bread loaf and place it atop sandwich, pressing lightly. Cut crosswise in 4 pieces.