Heat a saucepan over medium heat and add the vegetable oil. Whisk in the flour and all seasoning ingredients, stirring until a smooth, paste-like base forms. Slowly pour in the broth, whisking continuously until the sauce is smooth. Reduce the heat to low and simmer for 10–15 minutes, until slightly thickened. Remove from heat. (The sauce can be made a day ahead and refrigerated overnight.)
In a large bowl, combine the ground venison, ancho chile powder, cumin, coriander, oregano, garlic powder, and kosher salt. Using your hands, gently form the mixture into 10–12 evenly sized meatballs and set aside.
Preheat the oven to 400°F. Place a 12–14 inch cast iron skillet in the oven and preheat for about 10 minutes.
Carefully arrange the meatballs in the hot skillet and drizzle the tops lightly with olive oil. Bake for 20 minutes.
Remove the skillet from the oven and pour the enchilada sauce over the meatballs. Top with shredded cheese, green onions, and cilantro. Return to the oven and bake for an additional 15 minutes, until hot, bubbly, and the cheese is melted.
Serve warm with sour cream and sliced avocado.