1. Rinse the lentils thoroughly under running water and pick out any debris.
2. In a medium saucepan, combine the rinsed lentils and 500 ml of water. Bring to a boil over medium heat, then reduce the heat and let it simmer for about 15 minutes or until the lentils are soft.
3. While the lentils are cooking, place the chopped pumpkin in another pot with a small amount of water (just covering the bottom) and steam on medium heat for about 10 minutes until soft.
4. Add the chopped bell peppers to the steaming pumpkin and continue to cook for an additional 5 minutes until the bell peppers become tender.
5. Once the lentils, pumpkin, and bell peppers are cooked, drain the lentils and add them to the pot with pumpkin and bell peppers. Stir to combine.
6. Allow the mixture to cool slightly before transferring it to a blender or food processor. Puree until smooth, adding a little bit of the cooking water if needed to achieve the desired consistency.
7. If you prefer a thicker texture, you can mix in a small amount of wheat flour while still blending to help thicken the puree.
8. Allow the puree to cool completely before serving it to your baby.

Summary:
This recipe is nutritious and packed with essential vitamins and minerals beneficial for your baby's growth and development. The combination of bell peppers, pumpkin, and lentils provides a good source of fiber, healthy carbohydrates, and protein, making it a well-rounded meal for lunchtime.

Storing Options:
You can store any leftover puree in an airtight container in the refrigerator for up to 3 days or freeze it in portions for up to 3 months. Always ensure to thaw and heat thoroughly before serving.

Possible Side Effects/Allergies:
While this dish is generally considered safe for babies, it's essential to introduce each ingredient individually before combining to check for allergies or digestive issues. Lentils may cause gas in some babies; monitor your child's reaction and consult a pediatrician if needed.