Hold tofu over the sink and gently squeeze out moisture. Blot surface dry with a paper towel (do not press). Slice tofu crosswise into 6 rectangular slabs. Slice slabs in half to create 12 squares, then cut squares in half diagonally to create 24 triangles.

Pour soy sauce on a plate. Mix together bread crumbs, onion powder, garlic powders, and thyme on a second plate. Set out a third plate. Dip each tofu piece in soy sauce, turning to coat; dredge in bread-crumb mixture, sprinkling tops with mixture and turning to coat. Set coated tofu on third plate.

Spray a large cast-iron or nonstick skillet with cooking spray and heat over medium-low heat. Working in batches of about 8 pieces, cook tofu, flipping with a thin spatula and spraying skillet between batches, until crisp and browned on most sides, about 5 minutes per batch.

For the dipping sauce, stir mustard, syrup, and oil together with a fork in a small bowl until smooth. If too thick, stir in warm water, 1 tablespoon at a time, until pourable.