1)
What is the comparison to an oven?
1.
Radak: An oven has fire and wood. The fire consumes the wood. So You should kindle [Your enemies] at the time of Your anger, so they will be finished, like an oven eradicates what is inside it. We find like this - "Shisemo ch'Galgal
2)
What is "l"Es Panecha"?
1.
Rashi: At the time of Your anger. Radak - this is like "u'Faneha Lo Hayu Lah Od" (Shmuel I, 1:18), "Pnei Hashem Chilkam" (Eichah 4:16).
3)
What is the tense of "b'Apo Yeval'em"?
1.
Rashi: It is a Tefilah.
2.
Radak: [Hashem tells David, you can make them like an oven, for Hashem with you;] He will swallow them and fire will consume them.