How do you manage your diet?

I have a question about my diet plan.

When planning your meals, do you eat diet meals for all three meals?

Do you decide on a diet meal plan for breakfast, lunch, and dinner?

Or would it be effective if I only ate a diet meal for dinner?

I'm trying to follow a diet plan, but I wonder if I should just eat small portions?

I'm wondering if I need to follow a separate diet plan to see results.