Combine teriyaki, ketchup, honey, vinegar, 3/4 cup water and cornstarch. Stir to combine. Set aside.
Heat oil in large skillet over medium-high heat. Add peppers and cook briefly, until slightly softened, about 5 minutes. Remove and reserve.
Add scallops to pan; sprinkle with 5-spice powder. Cook over medium-high heat until just cooked through, turning once, about 5 minutes. Add peppers back to pan. Pour in teriyaki mixture and cook, stirring, until thickened. Top with walnuts and serve over cooked rice.