Heat olive oil in a large skillet or wok over medium-high heat. Cook and stir garlic in hot oil until just fragrant, about 30 seconds. Add squash and zucchini, cook and stir until vegetables soften, about 7 minutes. Transfer squash mixture to a bowl.

Place skillet back over medium-high heat, place tofu pieces in the skillet, and top with brown sugar and soy sauce. Cook and stir until each side of tofu is golden brown, 3 to 5 minutes.

Return squash mixture to the skillet; cook and stir until heated through, about 3 minutes. Stir in Sriracha sauce and season with salt and black pepper.