1. Heat gas or charcoal grill. In gallon-size resealable food-storage plastic bag, mix oil, lime juice and taco seasoning mix until smooth. Add chicken; seal bag. Shake until chicken is evenly coated.
2. Place chicken on grill over medium heat. Cover grill; cook 12 to 15 minutes, turning once, until the juice of chicken is clear when the center of the thickest part is cut (at least 165° F). Let stand 5 minutes; cut into cubes.
3. Place the beans in a small pot and simmer on medium heat for 5 minutes.
4. Slice cherry tomatoes in half.
5. To assemble tostadas, layer each tostada shell with beans, guacamole, chicken, tomatoes, and Cotija cheese.
6. If cilantro and jalapenos are in your wheel-house, then top with a couple of cilantro springs and a few slices of jalapeno. Serve immediately.