Whisk the sugar, soy sauce, water, garlic, rice vinegar, Sriracha, and cornstarch together in a small bowl until the cornstarch is dissolved.

Heat half the oil in a large nonstick skillet over medium heat until shimmering. Add half of the tempeh strips and cook until they are deeply golden brown on both sides, about 3 minutes per side. Transfer the browned tempeh to a paper towel–lined plate and repeat the process with the remaining oil and tempeh.

Wipe out any excess oil from the skillet, then pour in the sugar-soy mixture. Simmer over medium-low heat until the sauce has thickened and reduced to about 1 cup, about 5 minutes. Transfer the cooked tempeh to a large bowl, pour half of the glaze over it, and toss gently to coat.

Lay the tortillas on a clean surface and divide the glazed tempeh evenly among them. Layer the bok choy, cilantro, radishes, and scallions on top, then drizzle each wrap with a tablespoon of the remaining glaze.

Fold the sides of each tortilla over the filling, then fold the bottom up and roll tightly to secure. Slice each wrap in half on a bias and serve immediately with the extra sauce on the side.