Chop onion, mince garlic, grate carrot, and slice pineapple; set all aside separately.
Add oil to a large skillet and heat over medium.
Add onion and garlic to hot skillet and sauté 2-3 minutes until fragrant.
Add carrots, chili powder, and cumin; reduce heat to low and cook for 5 minutes.
Drain and rinse beans; add to a medium-sized bowl and mash with the back of a fork.
Add mustard, tomato paste, and soy sauce to the beans, then add to the veggies. Cook for 1-2 minutes, then remove from heat.
Add oats, salt, and pepper to the bean mixture and mix thoroughly. When cool enough to handle, shape into 8 patties. (For best results, allow the mixture to chill completely in the fridge before handling.)
Spray a separate skillet or griddle with cooking spray; cook patties over medium until heated through and browned.
Meanwhile, add green beans to a small pan with a small amount of water; steam until crisp-tender, or simply cook in the microwave.
Serve each bean burger on a bun with pineapple slices and steamed green beans on the side.