Bell peppers become either crunchy or soggy
There is a slight carry over with most things you cook. However I think the answer to most "Why is my stir fry not like the restaurant's?" questions, has to do with heat. Their stoves are much, much more powerful. You simply can't get that with a typical home stove.

So, the way to get closest at home is to preheat your wok (or your largest flat, not non stick skillet) till it is screaming hot, add a bit of oil and cook your food in batches; No more than 1 layer and nothing crowding one another. Chef Ming Tsai suggests if you have a stainless steel wok that can go in the oven, to preheat it in there. 

It should sizzle and keep sizzling through your cooking. If it isn't, you are steaming it, which will cause your softer texture. The key to stir fry, is to cook it really quickly. With the smaller batches, it'll all cook pretty quickly that in the end it doesn't take that much longer.

Edit: You asked about blanching. You might blanch some harder vegetables, to cut down on stir fry time but I can't see that helping for peppers of any sort.