No worries on the onions iniQuity, they aren't nightshades. Tomatoes/peppers (included dry pepper spices)/eggplant/potatoes (not sweet potatoes though) are all nightshades.
That plan absolutely sounds like a primal person started it, or possibly paleo, though it doesn't make restrictions on fruits which paleo leans towards. No "modernly palatable" foods. I hope you get through and enjoy your 30 days!