Can I get the same result grinding the lentils with a food processor? I don’t have a spice grinder. Thank you,

There are several machines or methods you could use -
blender, processor, mortar and pestle, or the old reliable rolling pin on the ingredients in a plastic bag.
Just take care to go no farther than the texture recommended by the recipe - you don't want lentil dust, but a mixture of some pieces and some powder.