Remove stalk from Fennel and remove outer layer, cut in half and remove core from the bottom of the plant. Slice thinly and add to a mixing bowl
Remove ends and outer layer from the red onion and cut in half. Cut in half a second time and make small shaved knife cuts. Add 1/4 of the onion to your mixing bowl
Cut Avocado in half and remove pit. Cut each side into 1/2 inch slices and add to a mixing bowl (try to handle the avocado as little as possible to avoid a mushy final product)
Drizzle oil, lemon juice, salt, and pepper over the main ingredients and gently toss together until well combined. Taste for seasonings or additonal lemon juice. Serve room temperature over a bed of Baby Spinach