Whisk 1/3 cup cornstarch, 3/4 teaspoon salt and 1 teaspoon pepper in a large bowl. In a medium bowl, whisk the remaining 3 tablespoons cornstarch and 3 tablespoons water until dissolved. Toss the shrimp in the cornstarch-water mixture to coat. Remove, shake off any excess and transfer to the bowl of seasoned cornstarch. Toss well to coat.
Heat 1 cup vegetable oil in a large skillet over medium-high heat until very hot. Meanwhile, heat the remaining 1 tablespoon vegetable oil in a separate large nonstick skillet over medium-high heat. Add the bok choy to the nonstick skillet and cook, stirring, until crisp-tender, about 3 minutes. Stir in the oyster sauce and ginger, then add the quinoa and edamame. Stir until heated through, about 1 minute. Season with salt and pepper.
Working in two batches, cook the shrimp in the other skillet, turning, until lightly golden and crisp, about 1 minute per side. Remove to a rack set over paper towels to drain. Remove all but 1 tablespoon oil from the skillet, then add the garlic and jalapeño. Cook over medium-high heat, stirring, 30 seconds. Return the shrimp to the skillet and cook, tossing, 30 seconds. Divide the shrimp and quinoa mixture among plates. Serve with the chili sauce.