1 small sweet potato

6 tablespoons olive oil, divided

Kosher salt, freshly ground pepper

1 portobello mushroom

½ small zucchini

1 small shallot, finely chopped

¼ teaspoon crushed red pepper flakes

1 cup cooked quinoa (from about ½ uncooked)

¾ cup dried breadcrumbs

1½ teaspoons fresh lemon juice

4 English muffins, split, toasted

Guacamole, tomato chutney, and sprouts (for serving; optional)