Vegetarian Mushroom Meatball Subs

What you will need

½ teaspoon extra-virgin olive oil, more for drizzling

½ yellow onion (about 1 cup chopped)

8 ounces mushrooms, de-stemmed, chopped

1 cup cooked black beans, drained and rinsed

2 large garlic cloves

1 tablespoon balsamic vinegar

1 tablespoon tamari

½ cup walnuts

1½ cups cooked brown rice

½ teaspoon chili powder

½ teaspoon onion powder

½ teaspoon sea salt, or to taste

½ teaspoon freshly ground black pepper

1 cup panko bread crumbs

6 soft sub buns or sliced soft baguette

2 cups jarred or homemade marinara sauce

½ cup chopped fresh basil

Several handfuls of arugula, optional

Parmesan cheese, optional