Short answer: Only a very simple version is acceptable, and only if it matches your pachchakkhan (vow) and your Sangh’s maryādā.

Guidance by common Jain practice in Paryushan:

• Not allowed if you are doing aymbil/aayambil, upvās with nirjal/boiled water only, or any pachchakkhan that forbids rasa/spices/oil. Lemon rice (even plain) is not permitted in these.

• If you are on simple ekāsan/biyasanu with “no greens, no roots, fresh food before sunset, boiled water”:

• Allowed: plain steamed rice mixed only with a little fresh lemon juice and salt. • Avoid: all tadkā/tempering (oil/ghee, mustard seeds, curry leaves, peanuts, turmeric, chilies, hing, sesame, etc.). Also avoid any green leaves and root vegetables. Prepare fresh the same day, before sunset, using boiled/filtered water.

Tradition notes:

• Shvetāmbara Paryushan: Many keep stricter “no-green” and very simple food; follow your local Sangh/Guru’s instructions.
• Digambara Das-Lakshan: Many observe ekāsan or aymbil-type restraints; in those, lemon rice is generally not allowed.

When in doubt, keep it plainer: plain rice + a few drops of lemon + salt, fresh and before sunset, only if your pachchakkhan permits.