Cook pasta according to package directions, omitting salt and fat. Drain; place in a large bowl.
Melt butter in a large nonstick skillet over medium-high heat. Add zucchini, squash, and peas; sauté 2 minutes or until crisp-tender. Stir in tomatoes; sauté 30 seconds. Add vegetable mixture and 1/2 cup Cilantro Pesto to pasta, tossing gently to coat.
Sprinkle salt and black pepper evenly over tuna. Return skillet to medium-high heat. Coat pan with cooking spray. Add tuna to pan; cook 2 minutes on each side or until desired degree of doneness. Slice tuna across grain into 1/2-inch-thick slices. Spoon about 1 cup pasta mixture onto each of 6 plates; top each serving with 1 sliced tuna steak.
Note: Nutritional analysis includes Cilantro Pesto.