Add soy sauce, mirin, sriracha, rice vinegar, brown sugar, minced garlic, minced ginger, black pepper, and 1 tsp white pepper to a medium bowl and stir until combined.
Add sesame oil to a large skillet, pot, or wok and on medium-high heat. When sizzling, add all vegetables, garlic powder, 1 tsp white pepper, salt, and water. Stir to coat and cover for 5-7 minutes or until vegetables are brightly colored.
Remove vegetables and set aside.
Add shrimp and teriyaki sauce to the same hot pan/pot/wok. Cook for 10-12 minutes or until shrimp are pink and plump.
Remove shrimp only (leaving sauce) and set aside with vegetables.
Simmer sauce until thick. (Add 1 tsp cornstarch + ¼ cup water if it’s not thickening/you’re impatient like me.)
Remove from heat. Return vegetables and shrimp to the pan/pot/wok with the thickened sauce and toss until coated.
Serve with rice or riced cauliflower, garnished with sesame seeds or chopped scallions.