Steam broccoli and cauliflower florets or cook them in boiling water for 5-6 minutes or until broccoli florets are bright green. Remove from the heat and transfer them into cold water. Drain and set aside.

Preheat oven to 375F. In a large bowl, whisk together the egg, milk, Greek yogurt, olive oil, ¾ of the cheese, salt and pepper.

Add in the cooked cauliflower and broccoli florets and stir well. Pour it in a small casserole pan and bak efor about 40 minutes or until slightly golden. Optionally, you can remove it after 40 minutes, sprinkle little extra cheese and bake for another 5 minutes.

For the onion topping, heat olive oil in the same pan you boil the florets. Make sure you dry it first. Add the onions and saute over medium-high heat, stirring occasionally for about 5 minutes or until they are golden and Brown around the edges.

Top the baked casserole with sauted onions and then serve.