Pour the bottle of Lawry's Baja Chipotle (or mesquite) marinade over the 4 boneless chicken breasts in a shallow dish or resealable bag; refrigerate and marinate for at least 30 minutes or up to overnight.
Preheat a grill or grill pan to medium-high. Remove the chicken from the marinade and grill until the internal temperature reaches 165°F (74°C) and the chicken is cooked through; set aside and keep warm.
While the chicken grills, heat 1 Tbsp olive oil in a large saucepan over medium heat. Add 1 cup orzo and cook, stirring constantly, until the orzo is lightly browned.
Stir in 2 tsp Southwest seasoning (or chili powder) and 2 Tbsp tomato paste, then add 2 cups chicken broth and bring to a boil.
Reduce heat to low, cover the pan, and simmer the orzo for 15 to 20 minutes until the liquid is absorbed and the orzo is tender; fluff with a fork.
Combine the diced 8-oz Velveeta and the undrained 10-oz can of diced tomatoes and green chilies in a medium microwave-safe bowl. Heat on HIGH in 30-second intervals, stirring between intervals, until the cheese is fully melted and smooth.
To assemble, divide the orzo into four plates, top each with a grilled chicken breast, and spoon about 3 to 4 Tbsp of the queso over each serving. Serve immediately.