Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the penne and return to a boil. Cook the pasta uncovered, stirring occasionally, until the pasta has cooked through but is still firm to the bite, about 11 minutes. Drain well in a colander set in the sink. Rinse with cold water to stop the cooking process.
Combine the mayonnaise, salad dressing, Italian herbs, garlic powder, cayenne pepper, salt and pepper in a blender; blend until completely mixed.
Place the coleslaw mix, tomatoes, cucumber, tuna, Cheddar cheese, spring onions and the cooked pasta in a large bowl; pour mayonnaise mixture into the bowl; toss to coat. Serve cold.