To make the BBQ sauce, whisk together all ingredients to a medium pot until smooth. Bring to a gentle simmer for about 5 minutes. Transfer to a jar.
In a large skillet over medium-high heat, warm enough oil to generously coat the pan. Once the oil is hot, add the tempeh and cook, undisturbed, for about 3-4 minutes, or until golden brown. Give it a stir and cook for 1-2 more minutes.
Reduce the heat to low and stir in the BBQ sauce for about 15-30 more seconds. If your pan is still super hot, the sauce will bubble rapidly so be careful!
Warm the tortillas. Top with lettuce, tempeh, cheese, corn, avocado, sour cream or yogurt, cilantro (if using), and a squeeze of lime.