Make the cilantro ranch dressing: in a mixing bowl combine ranch dip mix, mayonnaise, sour cream, minced garlic, chopped cilantro, diced jalapeño, and milk; whisk until smooth and adjust milk for desired consistency.
Prepare the chicken: heat 1/4 cup vegetable oil in a skillet over medium heat.
Add the cubed chicken to the skillet and season with garlic salt, black pepper, cumin, and oregano.
Cook the chicken, stirring occasionally, until no longer pink in the center and cooked through, about 6–8 minutes depending on piece size; drain any excess oil and set chicken aside.
Assemble the bowls: divide cilantro lime rice among four bowls (about 1 cup rice per bowl), then top with chopped romaine, corn, black beans, diced tomatoes, avocado, and cooked chicken.
Drizzle each bowl with the cilantro ranch dressing and sprinkle with chopped cilantro leaves; serve immediately.