Mix almond flour, almond butter, eggs and sea salt in a small bowl.
Cover a baking sheet with 2 tsp olive oil, then spread the mixture over it, making a 1/4" thick crust. Bake for 10 minutes.
Meanwhile, add the remaining olive oil, onions, mushrooms, and sliced sausage to a large skillet over medium-high heat until the sausage is browned and the onions are slightly translucent. Remove from skillet and set aside.
Add garlic and red pepper to the skillet. Sauté the vegetables for a few minutes, or until slightly tender. Note: do not cook the vegetables entirely in the skillet or they will be too soft when cooked on the pizza.
Remove the crust from the oven and cover with marinara sauce. Add the sausage and sautéed vegetables. Sprinkle with oregano and fennel seed, then bake for 20-30 minutes.
Remove from oven when fully cooked and top with sliced tomatoes.
Carefully lift the slices out of the pan as the dough will still be soft.