Heat a large skillet on medium heat. Add the oil. Add the onion as soon as a little piece gently sizzles in the oil. Sautè, stirring frequently for about 5 minutes or until onion starts getting translucent.
Add the mushrooms, garlic and sea salt. Sautè 2 minutes.
Add the daikon greens and stir until the greens get coated with the oil and onions. Add a Tbsp or two of water. Cover and let cook until tender, 3-4 minutes.
Remove from heat. Add a squeeze of lemon juice at the table.