Many of our users have the weekly planner suggest only dinners, and then handle the rest of their meals on their own. You can do this by removing the other meals from your "Weekly planner layout" (found in the "Settings" menu), and then regenerating the weekly plan to match the new layout.
If you want just one meal, you'll need to make sure you change your nutrition targets to match that one meal. For example, if I just want dinner every day, I set up my profile to give me around 400 calories with my desired macros.
More info in our how-to: