Place a steam rack in a 6-qt. electric or stove-top pressure cooker. Add 1 cup water to pot. In a 1 1/2-qt. round ceramic or glass baking dish combine the first seven ingredients (through garlic). Cut three double-thick, 18x3-inch heavy foil strips. Crisscross strips; place dish on crisscross. Transfer dish to steam rack using the strips. Fold strips down inside pot. Lock lid in place. For an electric cooker, cook on low pressure 7 minutes. For a stove-top cooker, bring up to pressure over medium heat; reduce heat to maintain steady (but not excessive) pressure 7 minutes. For both models, let pressure release naturally 15 minutes. Release any remaining pressure. Open lid carefully. Stir mozzarella cheese into dip. Let stand, covered, for 10 minutes; stir. Use foil strips to lift dish out of pot. Sprinkle with Parmesan cheese. Top with pesto. Serve with toasted bread slices.