Working over a gas flame, on a grill or under a broiler preheated to high, char the poblanos, turning often, until the skins are blackened all over, 5 to 10 minutes. Place in a bowl, then cover and let sit until cool enough to handle, about 15 minutes. Using paper towels, peel off the skins. Seed and slice the poblanos.
Meanwhile, in a medium bowl, whisk the cilantro, lime juice, olive oil, sesame seeds, coriander, cumin, agave, granulated garlic and onion and the oregano; season the dressing with salt and pepper.
Preheat a grill or griddle over medium-high. In another medium bowl, season the chicken and add half the dressing; turn chicken to coat. Grill, turning occasionally, until the chicken is charred in spots and cooked through, 10 to 12 minutes. Slice the chicken; transfer to a plate. Drizzle with more dressing.
Grill the tortillas until charred in spots, about 1 minute per side. Fill the tortillas with the lettuce, radishes, poblanos, sliced chicken, avocado, onion and more dressing as needed.