Place the chopped onions and minced garlic in a 4-quart slow cooker.
Cut the steak into 2-inch pieces, then toss with chili powder, salt, and pepper.
Add the seasoned meat to the slow cooker.
Top with salsa, cover, and cook on low for 8–9 hours, or until the steak is tender.
Remove the meat from the slow cooker and shred using two forks.
Return the shredded beef to the slow cooker along with the sliced bell pepper and summer squash.
Cook on high for 30–40 minutes, until the vegetables are tender but still slightly crisp.
Notes / Tips / Wine Advice:
Serving Tip:Serve warm with flour tortillas, sour cream, and your favorite garnishes such as guacamole, shredded cheese, or lime wedges.Wine Advice:Pair with a light-bodied red wine like Grenache or a refreshing white like Sauvignon Blanc.