Heat the oil in a large skillet with a tight-fitting lid over medium-high
heat; add onion, mushrooms, basil, and fennel seeds and sauté until onion is translucent.
Stir in frozen mixed vegetables and continue to cook until veggies are heated through (drain off excess liquid as necessary to speed up cooking time, if you’d like).
Spread cooked veggies evenly on the bottom of the skillet; salt and pepper to taste; arrange fish fillets on top of veggies then place tomato slices on fish. Reduce skillet heat to medium then cover and cook for 10 to 15 minutes or until fish flakes easily when tested with a fork.
Sprinkle Parmesan cheese over tomatoes and cover for a few minutes to heat through and slightly
melt. Serve hot.