Drain and finely chop the marinated artichoke hearts. Place them in a medium bowl and set aside.

In the same bowl with the chopped artichokes, add mayonnaise, grated Parmesan cheese, and garlic powder. Mix well until all ingredients are thoroughly combined.

Fold in the halved cherry tomatoes and diced red onion into the artichoke mixture. Stir gently to combine without breaking the tomatoes.

Brush both sides of each bread slice lightly with olive oil. Toast in a skillet over medium heat for 2-3 minutes per side until golden brown and crispy.

Spread a generous amount of the artichoke mixture on 4 slices of toasted bread. Top each with a handful of fresh arugula.

Place the remaining toasted bread slices on top to complete the sandwiches. Cut each sandwich in half diagonally and serve immediately while the bread is still warm.