Press the firm tofu for about 15 minutes to remove excess water, then cut into small thick triangles.
Wash the eggplant and bell pepper. Cut the eggplant into large chunks with the peel on and cut the bell pepper into large chunks.
Peel and mince the garlic and ginger.
In a small bowl, whisk together sriracha, sesame oil, rice vinegar, soy sauce (or tamari), sweet chili sauce, hoisin sauce, vegetable broth, cornstarch, salt, and black pepper until smooth to make the sweet & spicy sauce.
Heat a large skillet, wok, or non-stick frying pan over medium-high heat and add the vegetable oil. Add the tofu and fry, turning occasionally, for 6–8 minutes until all sides are golden and slightly puffy; transfer to a paper towel-lined plate to drain.
In the same pan, sauté the minced garlic and ginger in the remaining oil over medium heat for about 1 minute until fragrant.
Increase heat to high and add the eggplant and bell pepper. Stir-fry for 6–8 minutes, adding additional oil by the tablespoon if the eggplant soaks up the oil and the pan becomes dry.
Pour in the prepared sweet & spicy sauce and cook, stirring, for 2–3 minutes until the cornstarch activates and the sauce thickens and glazes the vegetables.
Add the fried crispy tofu back to the pan, toss gently to coat with the sauce, heat through, then remove from heat and serve.