Wash the lentils and barley. This means putting them in a strainer and running water over them a bit. Jiggle the strainer around a bit so that they all get wet. Remove any stones.
Put the lentils, rice, onion, and bay leaf in a crock pot.
Drain the liquid from the diced tomatoes into a big measuring cup. Add enough water to make 4 cups (1000 mL). Pour the mixture into the crock pot and stir well.
Cook on high power for 3 hours of low power for 6 hours. It should be quite dry but soft.
Add the tomatoes, salt, and chili powder and stir well. Adding the salt earlier may interfere with the lentils cooking properly for some reason.
If you are not ready to eat yet, leave the mixture in the crock pot at low power.
Remove the bay leaf before serving.
Note:
The liquid will not boil away with time. If there is a little bit too much, leave it in as the mixture will thicken as it cools. If there is a lot (like soup), you should drain it off.