To roast garlic see this tutorial.

Pierce potatoes and place in the microwave for 8 minutes on high each side, so that's 16 minutes. Remove from microwave and cool in room temperature.

In a bowl, lightly mash beans, add egg, flour, salt, pepper, minced roasted garlic, and cumin. Mix, then place in the fridge for 10-15 minutes as this will help forming the mix into patties.

In another small bowl, add yogurt, minced roasted garlic, pepper, and salt. Lightly mix and cool in the fridge.

Heat a pan on medium heat and add a little bit of olive oil. Form sweet potato mixture into 4 equal patties and fry until both sides are golden.

Place patties in bread buns, top with yogurt sauce, sliced avocados, tomatoes and bell peppers.