Once you've built your first day, you can fill in the rest of the week fast, no need to rebuild every meal.
On the day you want to reuse, switch to the Day view and click the Copy icon.

You'll see a "Meal plan has been copied" confirmation at the bottom of the screen.

Now hover over the day where you want it and click Paste meal plan. Everything is copied over, the name, description, thumbnail, all meals, and even the meal alternatives.