Bring a medium pot of water to a boil. Add 2 to 3 cups trimmed snap peas and 2 red bell peppers (cut into ~1-inch strips). Boil 2 to 3 minutes until crisp-tender, then drain and set aside.
While the vegetables cook, heat a large skillet or wok over medium-high heat.
Add 3 tablespoons sesame oil to the hot skillet. When the oil is hot and shimmering, add 1 large sweet onion, sliced. Cook, stirring frequently, until the onion is slightly charred and tender, about 5–7 minutes.
Stir in 2 cloves minced garlic and cook until fragrant, about 30 seconds.
Add the drained snap peas and red pepper strips to the skillet, stir to combine, and cook for an additional 2 minutes.
In a small bowl, whisk together 1 tablespoon chili garlic sauce, 1/4 cup soy sauce, 1 teaspoon minced ginger, and 1 teaspoon corn starch until the corn starch is fully dissolved.
Add 1 1/2 lbs raw shrimp (peeled and tails removed) to the skillet and cook, tossing, until the shrimp begin to turn pink, about 1–2 minutes.
Pour the sauce into the skillet and toss to coat everything. Continue cooking, stirring, until the shrimp are opaque and cooked through and the sauce has thickened, about 1–2 minutes.
Remove from heat and serve immediately.