Heat the grill on high for at least 10 minutes. In a bowl, add the chicken, olive oil, and ½ teaspoon salt and toss to coat. Grill the chicken for about 5 minutes per side, or until cooked through. Once cooked, slice, chop or shred up the chicken.
In a small pot over medium-low heat, add the butter and red pepper flakes and melt the butter. Once the butter has melted and starts bubbling on the edges, let it keep bubbling gently to toast those spices for 30 seconds to 1 minute, then remove from heat and let it cool for a few minutes. Transfer to a high-speed blender.
In the blender along with the butter, add the tomato paste, soy, vinegar, garlic, and remaining 1 teaspoon salt and blend until smooth.
Pour the sauce into a large bowl. Add the chopped grilled chicken and toss to coat.
Rinse out the blender and add the yogurt, blue cheese, vinegar, and salt and blend until combined (you want it a little chunky). If it won’t blend easily, add a splash or two of water or more yogurt. You could also just mix it together in a bowl if you crumble your blue cheese really finely.
Warm your tortillas and top with buffalo chicken, lettuce, tomatoes (if using) and top with the blue cheese sauce and cilantro.