Whisk olive oil, 25g fresh coriander, chilli powder, garlic, lime juice and salt together in a bowl; add prawns, toss to coat and marinate in the fridge for 20 minutes.
Heat a large pan over medium-high heat; lightly grease pan. Add onion, green pepper and chilli pepper; saute until tender, 10 to 12 minutes. Transfer vegetables to a bowl and cover with foil to keep warm.
Pour prawns and marinade into the same pan over medium-high heat; cook until prawns are pink and opaque, about 2 minutes per side. Stir vegetables into prawn mixture; cook and stir until heated through, 2 to 3 minutes.
Spoon prawn-vegetable mixture onto tortillas and top each with Cheddar cheese, lettuce, soured cream, tomatoes and remaining chopped coriander.