Bring a large pot of salted water to a boil. Add the tortellini and cook as the label directs; drain and set aside. Meanwhile, combine the tomatoes, olives, cucumber, artichokes and reserved mozzarella in a large bowl. Add the vinegar, Italian seasoning and 2 tablespoons olive oil and toss well.
Season the steak generously with salt and pepper. Heat a large skillet over medium-high heat; add the remaining 1 tablespoon olive oil and heat until shimmering. Add the steak and cook until well browned, 3 to 5 minutes per side for medium-rare. Remove to a cutting board and let rest, 5 minutes. Slice the steak.
Add the scallions and cooked tortellini to the tomato mixture and toss until coated. Season with salt and pepper. Divide among bowls and top with the steak.