To make sauce, in medium bowl, whisk together all sauce ingredients. Set aside.
To make stir-fry, start by cutting tofu into bite-sized cubes. Allow cubes to sit on clean tea towel or paper towel-lined plate for about 10 minutes to get rid of excess water.
In medium bowl, whisk together tamari, chili sauce, sesame oil, and maple syrup. Add tofu and toss to coat in sauce. Set aside for 4 to 5 minutes, tossing occasionally.
In another medium bowl, add cornstarch. Using fork, transfer cubes of tofu into cornstarch and toss to coat.
In large cast iron skillet over medium heat, warm 1 Tbsp (15 mL) grapeseed oil. Using fork again, transfer coated tofu cubes to pan, leaving any excess cornstarch behind. Cook tofu, turning frequently, until golden brown on all sides. Once evenly browned, transfer to plate and set aside.
Return skillet to burner and increase heat to medium high. Add remaining 1 Tbsp (15 mL) grapeseed oil and allow to warm for a minute before adding broccoli and sautéing for 1 minute. Add edamame and green onions and continue to sauté until broccoli is crisp-tender and edamame are warm, another 1 to 2 minutes. Add sauce, tofu, and red pepper flakes. Continue to stir-fry, stirring frequently, until sauce has evenly coated everything and has thickened slightly, about 1 to 2 minutes. Remove skillet from heat, add sesame seeds (if using), and toss to incorporate. Serve, while hot, over quinoa, if desired.