Pre-heat the oven to 400degrees F.
First, make the quick pickled red onions. Combine vinegar, water, salt and sugar in a small saucepan and bring to a simmer while stirring to dissolve sugar. Place onion slices in a mason jar and pour mixture on top. Let sit at room temperature for at least 30minutes before eating, or let cool completely and refrigerate in a sealed mason jar. Make up to 1 week ahead of time.
Toss the chickpeas in olive oil and then spices and place on a sheet pan in a single layer. Roast for 20 minutes, or until browned and crunchy, tossing half way through. Set aside.
While the chickpeas are roasting, make the green tahini by blending all ingredients together in a food processor. Adjust seasoning to taste. Depending on how thick your tahini is you may want to add a little water to thin the sauce out.
Now, make the sandwiches! Slice pitas in half and spread with green tahini. Spoon in chickpeas, avocado, pickled onions, and mint leaves. Eat up!