Learn Spanish (Latin America): Nosotros rellenamos la empanada como tú quieras.

We use the subjunctive quieras after como because the specific way you want the empanada stuffed isn't known yet. It is an open-ended offer. If we said como tú quieres (indicative), it would state a known fact: "We are stuffing it the exact way that we already know you want it."

Why does como translate to "however" instead of "like" or "as"?

When como is followed by a verb in the subjunctive, it sets up an unspecified condition. It literally means "in the manner that you might..." or "any way that you...". In English, this idea is most naturally translated using "however."

What is the difference between rellenar and llenar?

Both mean "to fill," but rellenar specifically means "to stuff" (like an empanada, a turkey, or a pillow) or "to refill" (like topping up a glass of water). Llenar is the more general word for "to fill," like filling a room with people or a bucket with water.

Since rellenamos is the same in both present and past tense, how do we know this is present tense?

We know it's present tense because of the second half of the sentence. The present subjunctive quieras points to a present or future choice. If this were a past tense sentence ("We stuffed the empanada however you wanted"), it would require a past subjunctive verb at the end, like como tú quisieras.