Put cornstarch in a large bowl and add shrimp; toss until shrimp are covered.
In a large pan, heat oil over medium-high heat. Make sure the oil is hot before adding shrimp. Then, add the shrimp in batches to avoid overcrowding the pan and reducing the heat. Cook until the shrimp are done (about 1 - 1 1/2 minutes per side).
In a medium bowl, combine mayonnaise, yogurt, Thai chili sauce and Sriracha. Stir to combine.
Toss shrimp in the sauce mixture. In a tortilla boat, add coleslaw mixture or lettuce. Top with shrimp and, if desired, drizzle with Tex-mex ranch dressing.