Preheat oven to 375F.

Add 2—3 Tbsp. water to a medium Non Stick Frying Pan and heat over medium. Once water is simmering, add mushrooms and cook, stirring and flipping often, until softened and liquid has evaporated, 3—5 minutes. Cooking mushrooms in water first helps them release their moisture and concentrates their flavor without adding greasiness.

Add oil, shallot, and season with salt and pepper. Cook, stirring, until mushrooms start to brown and shallot is softened, about 2 minutes.

Add tomatoes and cook, tossing occasionally, 2 minutes. Add greens and cook until just softened, about 2 minutes more. Taste and adjust seasoning.

Pour eggs into pan and season with ¾ tsp. salt and a few grinds of pepper. Stir in Parmesan.

Cook, stirring occasionally and scraping the bottom of the pan in small circular motions with a silicone or wooden spatula to encourage the eggs to cook evenly. Tilt the pan and lift the edges of the frittata to allow liquid eggs to flow under the cooked eggs. Continue to cook until eggs are starting to set around the edges, about 5 minutes.

Transfer pan to oven and bake until eggs spring back to the touch and are set all the way through, 10—12 minutes. Carefully insert a paring or butter knife halfway into the center to check for doneness, no runny egg should remain.

Transfer frittata to a large Plate or Butcher Block, top with extra Parmesan, flaky salt, pepper, and herbs, if desired. Slice into wedges to serve.