1. Combine sour cream and Dijonnaise in a small bowl.
2. Place crackers in a food processor; process until fine crumbs measure 1 cup. Place crumbs in a shallow dish. Place flour in another shallow dish. Sprinkle fish with salt and pepper. Dredge 1 fillet in flour. Dip in egg substitute; dredge in crumbs. Repeat procedure with remaining 3 fish fillets, flour, egg substitute, and crumbs.
3. Heat oil in a large nonstick skillet over medium-high heat. Add fish to pan; cook 4 minutes on each side or until fish flakes easily when tested with a fork or until desired degree of doneness.
4. Spread 1 1/2 teaspoons sour cream mixture on each half of 4 rolls; place 1 fish fillet on bottom half of each roll. Top each serving with 2 tomato slices, 3 onion slices, 1 romaine leaf, and top half of roll.