We personally really like using ground beef in this recipe because of the flavor it gives to meatballs. But, I get it. Ground beef is getting expensive and some people just choose not to eat it. So yes, if you want, you can swap the ground beef for ground turkey or ground chicken. If you do, the taste will be off so I suggest adding a half to a whole tablespoon of Worcestershire sauce into the meat mixture. That helps ground poultry taste more like ground beef. Keep in mind that those are both leaner than beef, so the recipe won't be as juicy. In that case, you may want to pre-bake the peppers for about 20 minutes before stuffing them, then cook the stuffed peppers about 25 minutes. That should be long enough for the peppers to soften but not too long that the turkey or chicken dries out. That time may need to be adjusted based on your oven, so keep checking and pull the peppers out of the oven when the chicken or turkey has reached 165 F.