Brush mushroom with olive oil and grill, turning every couple of minutes, for 4-5 minutes. Allow to cool, chop coarsely and set aside.
In large skillet, heat butter over medium-high heat.
Whisk eggs, salt, and pepper in a bowl and add to skillet; cook, stirring occasionally, until large curds form, 3-4 minutes, then gently stir until eggs are almost set.
Using a rubber spatula, pat eggs into an even layer.
Add microgreens and musrhooms to top of one half of omelette.
Slide half the omelette onto a plate and using spatula, fold remaining omelet over the filling; garnish with additional micrgreensl.
Notes
Sautee mushrooms in skillet in lieu of grilling them.