Place top oven rack in center position and preheat oven to 400°F. Line a large, rimmed baking sheet with parchment paper or a Silpat® baking mat. Set aside.
Whisk together the tamari, rice vinegar, sesame oil, honey, garlic powder, ginger, and crushed red pepper flakes in a medium bowl. Season with salt and black pepper, to taste, and stir to combine.
Combine broccoli, peppers, and onion in a large bowl and pour two-thirds of the sauce on top. Toss until vegetables are evenly coated before spreading into a single layer without overcrowding onto the prepared baking sheet.
Place baking sheet in preheated oven and roast for 20 minutes, or until vegetables are crisp and tender and starting to develop a bit of color. Remove from oven and set aside.
While the vegetables are roasting, toss the shrimp with the remaining sauce in the same mixing bowl. Season with additional salt and black pepper, if desired, and set aside.
When the baking sheet has cooled slightly, pour shrimp onto the sheet and carefully spread into a single layer among the veggies without overcrowding.
Return baking sheet to oven and roast for another 5-6 minutes, or until the shrimp is cooked through and opaque. Do not overcook the shrimp.
Remove from oven and cool slightly. Top with a squeeze of fresh lime juice, some toasted sesame seeds, and sliced green onions before serving.