Vegan Teriyaki Black Bean Burgers with Grilled Pineapple

I medium sweet potato

cooked black beans

oat flour or rolled oats that have been ground in a food processor or blender, plus more if needed

scallion, thinly sliced

garlic, minced

tamari

pineapple juice

sesame seeds

freshly grated ginger

toasted sesame oil

cornstarch

neutral-flavored vegetable oil

red onion, sliced into rings

pineapple rings

burger buns

Lettuce leaves

Tomato slices

Spicy vegan mayo, optional