Google is sending me Recipe Metadata Warnings
Warnings are not problems but recommendations
While getting emailed about warnings can seem like a big issue, they aren't something to immediately worry about. You basically get a warning if you haven't filled in a field that Google does want to see in the recipe metadata.
It's basically a recommendation on how you can make your recipes even better.
Warnings can usually be resolved by filling in the fields Google is telling you about. For example: adding nutrition facts (just calories is enough), a recipe video, ...
Can I just tell Google I don't have these fields?
If you don't plan on ever adding recipe videos it can be annoying to keep getting warnings about this. Unfortunately the only way to not get these warnings is to actually fill in the fields. There is no way around this.
If someone is suggesting otherwise, be aware. Filling in bogus data in the recipe metadata will indeed get rid of the warning, but could get you in bigger trouble afterwards, if Google notices you're trying to cheat the system with false data.
I would recommend just ignoring these warnings. As mentioned above, they are just recommendations, not actual problems.
Are you seeing errors as well?
While "Warnings" are not uncommon, you should definitely be concerned if you are seeing "Errors" as well. These are actual problems with the recipe metadata and things you should look at immediately as they will prevent your rich snippets from showing up.
Checking your recipes for warnings and errors
An easy way to check for warnings and errors is to use the built-in Recipe Metadata Checker on the WP Recipe Maker > Manage > Recipes page. Just hover over the color in the SEO column and you'll see if anything is missing.