This is a regular verb. It follows the conjugation pattern of the verb hablar.
Present:
Engordo fácilmente si no cuido mi alimentación.
I gain weight easily if I don't watch my diet.
Preterite:
Después de las fiestas, engordamos un poco.
After the holidays, we gained a little weight.
Future:
Si sigo comiendo así, engordaré.
If I keep eating like this, I will gain weight.