Whisk together mayonnaise, feta, herbs, and lemon juice and spread over top of fish. Put 2 lemon slices (slightly overlapping) on center of each fillet. Drizzle lemon slices with remaining 2 teaspoons oil.
05Broil fish 8 inches from heat until just cooked through, 14 to 16 minutes. If topping browns before fish is cooked, cover loosely with foil. Serve fish with tomatoes.