For the crust: Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper and brush with 2 teaspoons of the olive oil.
Add the sweet potato cubes to a food processor fitted with the blade attachment. Pulse until coarsely ground, similar to the texture of coarse salt.
Add the ground sweet potato, almond flour, Parmesan, salt, garlic powder and egg to a bowl and stir until combined. Transfer the sweet potato mixture to the prepared baking sheet and form into a 12-inch circle about 1/4 inch thick. Brush with remaining tablespoon olive oil. Bake until browned around the edges, 25 to 30 minutes.
For the toppings: Meanwhile, bring a pot of salted water to a boil. Prepare an ice water bath. Blanch the broccoli rabe in the boiling water, then transfer to the ice bath to stop the cooking process. Drain and set aside.
Set a medium skillet over medium heat. Add the sausage and cook, breaking it up with a wooden spoon into crumbles, until browned, about 8 minutes. Transfer the sausage to a plate with a slotted spoon.
Remove the crust from the oven and top with the pizza sauce, broccoli rabe, sausage, goat cheese and pepper flakes. Place back in the oven and cook until the toppings are warmed through and cheese is melted, another 8 to 10 minutes.