How to Make Sweet and Sour Tofu

Here's a little something for all you vegans and health nuts out there. Though I'm not a fan of tofu (or its preparation), this was pretty good.

Ingredients
14 oz. extra-firm tofu
1 small red onion
1 green bell pepper
1 red bell pepper
1 (1") piece ginger, peeled
2 garlic cloves, peeled
1/2 cup canned pineapple chunks, plus 1/3 cup pineapple juice, divided
1/3 cup low-sodium vegetable broth
3 Tbsp. unseasoned rice vinegar
2 Tbsp. reduced-sodium soy sauce or tamari
1 Tbsp. ketchup
1 Tbsp. light brown sugar
1 Tbsp. plus 1/3 cup cornstarch, divided
4 Tbsp. neutral oil, divided
Kosher salt
Steamed white rice, for serving
Sesame seeds, for serving (optional)