Place asparagus in a glass pie plate. Add 1/4 cup water and cover with microwave-safe plastic wrap, venting slightly at one corner. Microwave for 4 minutes.
In an 8 x 8 x 2-inch microwave-safe dish, add potatoes and 1/2 cup water. Cover with plastic wrap, venting. Microwave for 10 minutes. Season with 1/4 teaspoon of the salt.
Combine tomatoes, tomato sauce, peppers, oil, onion powder, dried oregano, garlic and 1/4 teaspoon salt in a microwave-safe 11 x 8 x 2-inch dish. Microwave, uncovered, for 5 minutes. Add tuna; spoon sauce over top. Cover with plastic wrap and vent. Microwave 3 minutes.
Rotate dish, uncover and turn fish over; spoon sauce over top. Re-cover and microwave for an additional 3 minutes. Tear in basil leaves. Let stand, covered, 5 minutes.
Serve tuna and sauce with room-temperature asparagus and
potatoes, gently reheating for a minute or 2, if desired.