Preheat oven to 400°. Unroll pizza crust and press to fit into a greased 15x10x1-in. baking pan, pinching edges to form a rim. Bake 10 minutes or until edges are lightly browned.
Meanwhile, in a large skillet, heat oil over medium-high heat. Add chicken and 1/2 teaspoon garlic; cook and stir until chicken is no longer pink. Remove from heat; stir in 2 tablespoons salad dressing.
Spread crust with 3 tablespoons salad dressing; sprinkle with remaining garlic. Top with half of the cheeses and all of the chicken. Sprinkle with remaining cheeses. Bake for 10-15 minutes or until crust is golden brown and cheese is melted.
In a small bowl, toss salad mix and green onions with remaining dressing. Just before serving, top pizza with salad and tomatoes.