Plain lentils sounds pretty boring.
We tried fresh fruit: mango, watermelon, kiwi fruit and banana – cut into pieces that she could hold in her hand. We allowed her to taste the food, but never required that she actually ate any. We had a constant watch on her, just in case she choked, and she sometimes did, but eventually she got the hang of eating. We never fed our girl mush, just proper food, and she ate what she wanted. This all started at 5 months.
The approach is called baby-lead weaning and it works wonders.
In contrast to what you seem to be trying to do, we never gave her mush, we gave her tasty food, and we never required her to eat it. She ate when she wanted to – she was breastfeeding the whole time to get the required nutrition.
A consequence of the whole process is that our daughter is a pretty good eater – she was really good for a while, but recently became picky, but not as bad as other kids.