Preheat oven to 375F and line a baking sheet with parchment paper.
In a small pan over medium heat add avocado oil. Once hot, add shallots, bell pepper and garlic. Sautee for a few minutes, stirring occasionally, until soft.
Meanwhile, in a large bowl mash the beans, leaving some chunks. Add in the sauteed veggie mixture and the remaining ingredients except for the cassava flour. Stir until combined.
Add in the cassava flour little by little until you reach a texture that is still moist but not too sticky.
Form into 4 thick patties and place onto baking sheet. Bake for 10 minutes, flip and then bake for 10 more minutes.