In a resealable plastic bag, combine the olive oil, garlic, herbes de Provence, salt, and pepper.

Add the beef cubes to the bag.

Refrigerate for at least 6 hours, or overnight, to marinate.

In a small bowl, combine the diced red onion, chopped sun-dried tomatoes, corn, and olive oil for the relish.

Refrigerate the relish until ready to serve.

Just before serving, add the diced avocado, crumbled feta cheese, and chopped parsley to the relish.

Gently toss the relish and season with salt and pepper to taste.

Thread the marinated beef cubes onto skewers.

Preheat grill to medium-high heat.

Grill the beef skewers for 5-7 minutes per side, or until cooked to desired doneness.

Serve the grilled beef skewers alongside the sun-dried tomato relish.