Preheat the oven to 400 degrees F. Line a baking sheet with parchment paper.
Sprinkle the shrimp with 1/2 teaspoon each of salt and pepper. Set aside.
Whisk the hoisin, soy, vinegar, Dijon, ginger, sesame oil and garlic together in a large bowl. Whisk in the vegetable oil. Add the bok choy to the bowl, then toss, then transfer them to one side of the baking sheet. Add the red pepper to the bowl, then toss in the remaining marinade, and transfer them to the center of the baking sheet. Toss the shrimp in the remaining marinade and arrange it on the last side of the baking sheet. Pour any remaining marinade over the vegetables and shrimp. Bake until the shrimp are pink and opaque and the vegetables are starting to char, 15 to 20 minutes. Remove from the oven and set aside. (The bok choy can be chopped into smaller pieces if desired.)
Divide the rice among 4 bowls. Add a few shrimp and the vegetables to each bowl. Top with the sesame seeds, scallions, peanuts, crunchy noodles and cilantro. Drizzle with the sriracha, if using. Serve warm!