Drain the tuna. Then break it up into small chunks in a small bowl. Add the sundried tomatoes, capers, carrots, and basil. Then add in the lemon juice, Italian seasoning, garlic powder, and whole grain mustard. Give it a mix to combine everything. Then add in the mayonnaise, starting with 1 Tbsp at a time. Mix is and then add more if necessary. You're looking for a consistency here where the mayo acts as a binder but doesn't make the tuna salad too creamy. It should still look relatively dry, but hold together.