Me encanta comer una quesadilla caliente con queso derretido.

In Spanish, verbs like encantar work much like gustar:

• The thing you love is actually the subject of the sentence.
• The person who loves it is shown by an indirect object pronoun. Here, me means “to me.”
• The verb agrees with what delights you. In “Me encanta comer una quesadilla…,” the entire action comer una quesadilla caliente con queso derretido is treated as a single idea (singular), so you use encanta.

Also, when you love doing something, you attach the infinitive directly—no de is needed (compare: Me encanta nadar, not Me encanta de nadar).

Una is the feminine singular indefinite article in Spanish. You use it because:

• quesadilla ends in -a, which makes it a feminine noun.
• You want to say “one (or a) quesadilla,” so you use una.

If you talk about more than one, you’d say unas quesadillas; for generic statements you can even omit the article and say Me encanta comer quesadillas…

In Spanish, the default position for most adjectives is after the noun they modify:

• una quesadilla caliente (a hot quesadilla)
• queso derretido (melted cheese)

You can sometimes move adjectives before the noun for emphasis or style, but after is the standard.