To prepare burgers, combine the first 9 ingredients in a large bowl or food processor. If you use a food processor, you don't have to dice the onion or mince the jalapeno pepper ahead of time. (This saves on cutting time if you have a good food processor). Transfer to a large bowl, and mix in the egg.
Put pinto beans and corn in the food processor, and then add to the mixture in the bowl. Alternatively, you can add the pinto beans/corn to the bowl and partially mash with a fork or potato masher.
Divide bean mixture into 4 equal portions, shaping each portion into a 3 1/2-inch patty, and refrigerate for 10 minutes.
Heat 1 tablespoon extra-virgin olive oil in a large skillet over medium-high heat. Add patties to pan, and cook 5 minutes on each side. Reduce to medium heat, cook an additional 5 minutes (flipping the burger patty once in between) to get a nice caramelized crust. Transfer burgers to a plate lined with paper towels.
Now it’s time for assembly! Place patties on bottom halves of buns; top each patty with 1-2 tbsp ketchup or bbq sauce, red onion slices, roma tomatoes, baby spinach leaves, and top half of bun.