Heat olive oil in a skillet over medium-high heat. Brown the beef cubes on all sides, then transfer them to the slow cooker.
In the same skillet, sauté onions and garlic until fragrant and translucent, about 3-4 minutes. Add to slow cooker.
Add cherry tomatoes, green beans, zucchini, beef broth, white wine, tomato paste, thyme, basil, salt, and pepper to the slow cooker. Stir gently to combine.
Cover and cook on low for 6-7 hours or on high for 3-4 hours until beef is tender and vegetables are cooked through.
If you prefer a thicker stew, mix cornstarch with 2 tablespoons cold water and stir into the stew 30 minutes before the end of cooking.
Garnish with fresh parsley before serving.
Notes
For an extra burst of summer flavor, serve with crusty bread or over a bed of fluffy couscous.