In a large skillet on medium heat, warm the sesame seed oil. When hot and shimmering, add onion slices and stir occasionally for 5 minutes.
While onions are cooking, peel and grate the ginger, crush and mince the garlic, zest and juice the lime, and seed and chop the jalapeño. Gather them all in a small bowl.
When onions start to brown and caramelize, add 2 tbsp of brown sugar and ¼ tsp of sea salt. Stir again, but not too often, to allow onions to caramelize further with the sugar.
While onions caramelize, chop bell peppers (sans seeds) and mushrooms, and gather in a bowl with the snow or snap peas.
Once onions look golden, limp, and browned--almost noodle-like--add to them the small bowl of ginger, garlic, zest, juice, and jalapeño. Stir and add another ¼ tsp of salt. (It's important to salt along the way rather than all at once!) Sauté this combination for 2-3 minutes. Then add the peppers, mushrooms, peas, and peanuts. Sprinkle in the remaining ½ tsp of salt.
Stir the contents of the pan and then allow to it cook unattended while you prepare the sauce, about 5 minutes.
In a small bowl (perhaps the one from the garlic-jalapeño mixture if you haven't put it in the sink yet...) whisk together sriracha, vinegar, soy sauce, peanut butter, coconut milk, fish sauce, and ground mustard. When vegetables are tender and soft, pour the sauce into the pan. Cook another 5 minutes or until sauce is thick and simmering.
Serve in large bowls with rice.