Spawning is not the issue - they may spawn even if only fed flakes.
The issue is egg and larva quality. Any food that provides the right nutrition will do fine.
As for getting them to spawn more quickly, I found live foods to be effective.
Anything that causes excitement - food or other fish will get them going faster.
A pair that lives in a dull environment or is bored all the time is less likely to spawn in my experience.
I think we have a similar mindset here, but feel it's worth clarifying since the guy is trying to learn.
The key in what you said is "any food that provides the right nutrition". I look at fish food similar to dog food (wife and I own a vet clinic). Sure you can feed your dog pedigree and think you're providing this great food (Known as Tetra Pellets in the fish world

), but the reality is you're either loading your dog up with things they don't need or things with little nutritional value (similar to iceburg lettuce for humans).
I don't feel there is any denying the closer we can get to feeding our animals what they eat in the wild, the better off we will be. This is true, but oftentimes people mistake an "all natural" diet with one full of all the nutritional value our animals need.
There are very few dog food companies I trust, and similarly there are very few fish food companies I trust. In my experience and research Thera A is a product worthy of my money. My last clutch of eggs was probably somewhere in the neighborhood of 200 (2nd clutch) and I haven't tried to rear any yet as I don't have the time due to a bathroom remodel.
Now that we have a true reason and not a suspected reason for the question I feel we can better answer it.
The pair i just got (only pair) is a proven pair (already spawned together). I have had them for about 2 or 3 weeks. How long until they spawn again in my tank?
The reality here is, when they're ready. Tank Params, Temp, food quantity, food quality, environment (including the smallest changes), stimulation...etc are all factors. Give your fish time to settle in, adjust to their environment, make sure you've got all your ducks in a row and chances are in your favor.