1) Set USD as primary currency and add EUR as supported currency.
2) Have linked bank accounts via Plaid that are USD and EUR.
3) Link American Express card via Plaid that's United States based.
4) Make EUR purchase with American Express card that's United States based.
5) Have Lunch Money automatically import these transactions via Plaid.
6) The EUR transactions are using the USD value as the EUR value, instead of the actual EUR value. For example: purchase was €50, shows $54.66 with €50 as the original purchase price (because it's an American credit card), Lunch Money shows €54.66 instead of €50 or $54.66.
Feel free to reach out for more info.