BBQ Hawaiian Tofu Bowl

large red onion ((cut into 1/4-inch slices))

red bell pepper ((seeded and cut into 1/4-inch slices))

plus 1 teaspoon olive oil ((plus more as needed) (divided))

block (14-ounce) extra-firm tofu ((drained and cut into 1-inch cubes))

sliced pineapple ((drained) (or 1 pineapple, peeled, cored, and cut into 1⁄4-inch slices))

barbecue sauce

package (5-ounce) baby spinach

cooked quinoa

Chopped fresh cilantro ((for garnish) (optional))