In a large skillet over medium heat, melt the butter.
Sauté the onion until slightly translucent, about 5 minutes.
Add the garlic and bell pepper, and cook for another 5 to 7 minutes.
Add the shrimp, and cook until pink, about 5 minutes. Throw in the cherry tomatoes, and stir them around for another 3 to 5 minutes, or until a few of them start to burst. Continuing to stir, drizzle the sesame oil over everything as you turn off the heat.
Serve the stir-fry hot, topped with the sesame seeds and scallions.