Place the spices in a medium bowl and whisk to combine. Use a paper towel to dry the shrimp and toss with the spices. Add in the chicken and use tongs to toss in the spices to coat everything evenly.
In a cast iron or large frying pan heat the vegetable oil or olive oil over medium high heat. Once the oil is hot, it will shimmer, place the chicken cubes in the pan and fry for about 5-6 minutes. Once the chicken has been frying for about 6 minutes, add the shrimp to the pan and continue to cook until the shrimp and chicken are both cooked all the way through.
Meanwhile, make the cabbage and avocado slaw.
Add the avocado, coriander leaves, lime juice, and fat-free Greek yogurt to the bowl of a food processor and blend until it's a smooth sauce. Taste and adjust the seasoning with sea salt and pepper. Using a sharp knife thinly slice the cabbage into ribbons and add to a large bowl. Spoon some of the avocado sauce into the cabbage and toss until well all the cabbage is coated well. Add as much or as little avocado sauce as you like.
To assemble the tacos:
Lay the tortillas flat and place some of the cabbage avocado slaw into the shell. Layer with some of the chicken and shrimp mix and drizzle with some more avocado sauce.