Cook the tofu: Toss the tofu with the soy sauce, garlic powder, cornstarch and black pepper until evenly coated. Heat a large skillet over medium-high heat and lightly coat with oil or cooking spray, if using. Cook the tofu for 8–10 minutes, turning occasionally, until golden and crispy. Transfer to a plate.
Cook the aromatics: While the tofu cooks, prepare the vegetables. In the same skillet, cook the onion for 4–5 minutes until softened. Add the garlic and ginger and cook for 30 seconds, then stir in the curry paste and cook for 1 minute until fragrant.
Simmer the curry: Add the sweet potato, bell pepper, coconut milk, vegetable broth and soy sauce. Stir well, bring to a gentle simmer, then cover and cook for 12–15 minutes, or until the sweet potato is fork tender.
Finish the curry: Stir in the cooked tofu, peas and spinach. Cook uncovered for 2–3 minutes, until the peas are heated through and the spinach has wilted. Remove from the heat and stir in the lime juice.
Serve: Divide between bowls over cooked jasmine or basmati rice. Garnish with fresh cilantro and lime wedges, if desired.