Im asking since I have directly added frozen peas to a flavor base with water. Its been over 30 minutes in simmering temperature with a lid and the peas are still not tender. They also stuck to the bottom of the pan.
There's no point in boiling peas separately if you can cook them in whatever dish you are making, it's an extra pan to clean up and you lose whatever flavor gets leached out in the cooking process. I think where you went wrong is adding them frozen as you caused the base to cool and they sank. If you add a lot of peas the base can take a long time to get back up to cooking temperature, which is why they haven't cooked.
Next time thaw them in hot water before you add them to the pot, this will make them cook much faster and it will get rid of any excess water from ice (some companies pack water with their frozen vegetables to bulk them out) which can dilute your food. The peas don't have to be warm or even up to room temperature, just not frozen anymore. Once you add them give them a stir or two every couple of minutes to keep them from sinking and burning on the bottom.
If you do want to add them to the pot frozen then you need to crank the heat up until the pot is back up to temperature.