Preheat the oven to 400°F (205°C) and grease a baking sheet with nonstick spray or a light coating of oil.
In a large bowl, toss the diced roma tomatoes, sliced yellow onion, and sliced bell peppers until evenly combined; spread the vegetables in an even layer on the prepared baking sheet.
In a small bowl, stir together the plain Greek yogurt, fajita seasoning, and minced cilantro to make a coating sauce.
Add the chicken strips to the yogurt mixture and toss until the chicken is fully coated.
Nestle the coated chicken strips among the vegetables on the baking sheet in a single layer.
Bake uncovered for 20–25 minutes, until the chicken is cooked through and the vegetables are fork-tender; internal temperature of chicken should reach 165°F (74°C).
With about 8 minutes remaining on the timer, wrap the tortillas in foil and place them in the oven to warm.
Remove the sheet pan and warmed tortillas from the oven, assemble fajitas with optional queso fresco, cilantro, lime, and extra Greek yogurt, and serve immediately.
