This is completely wrong - please never setup a framework like this.
Sorry to be so direct, but this is literally the essence of every single project/problem/case. Of course we have to identify ideas, figure out which ones are best, and prioritize. This is not what they're paying you millions of dollars to do as a consultant!
Rather, you have to break down how you are going to address the issue (i.e. how do you structure the ideas themselves).
How to Structure In General
I'm going to take a step back and answer the question you're really asking: How do I use frameworks in a case?
If there's anything to remember in this process, is that cases don't exist just because. They have come about because of a real need to simulate the world you will be in when you are hopefully hired. As such, remember that they are a simplified version of what we do, and they test you in those areas.
As such, remember that a framework is a guide, not a mandate. In the real-world, we do not go into a client and say "right, we have a framework that says we need to look at x, y, and z and that's exactly what we're going to do". Rather, we come in with a view, a hypothesis, a plan of attack. The moment this view is created, it's wrong! Same with your framework. The point is that it gives us and you a starting point. We can say "right, part 1 of framework is around this. Let's dig around and see if it helps us get to the answer". If it does, great, we go further (but specific elements of it will certainly be wrong). If it doesn't, we move on.
So, in summary, learn your frameworks, use the ones you like, add/remove to them if the specific case calls for it, and always be prepared to be wrong. Focus rather on having a view, refering back to the initial view to see what is still there and where you need to dive into next to solve the problem.
Structuring Growth Cases
In general, when looking for growth, I like the following general framework:
1) Improve existing business (i.e. look at our current products/customer segments to see where we can earn more $...higher q or p)
2) Grow our business through expansion of current products - this can be done either organically or inorganically
3) Grow our business by launching our existing products to new markets (i.e. new geographies, new customer segments, etc)
Now, how to talk about this in terms of structure, tailoring to the case, and the deeper level examples incl the why + how? I'll leave that to you to work through :P