This time you need more materials:

small bowl
white vinegar
baking soda
Spray bottle
scrub pad
Once you've gathered all the materials, you can start cleaning!

Remove the grill and set them aside. Clean the ones in the sink later (read more below).
Remove any debris from the bottom of the oven. That rubbish just gets in the way!
Combine baking soda and water in a small bowl to make a paste mixture. Start with baking soda, then slowly add water a few drops at a time until it's nice and thick. Depending on the size of your oven, you may need several batches of this mixture to fully coat the inside. If your mixture becomes too runny, just add more baking soda.
Spread the paste around the inside of the oven, covering the bottom and all sides. The baking soda may start to brown, which is fine. It just pulls up grease and dirt. Close the oven door and let it sit overnight, or at least 12 hours.
In the morning, wipe off the baking soda mixture with a paper towel to remove as much as possible.
Add white vinegar to a spray bottle and spray the inside of the oven, especially where there is baking soda residue. Then wipe it down with more scrubbing pads.
Now put the oven rack back and turn on the oven at 200 degrees for about 15 minutes to dry the oven.
Results of baking soda + vinegar
This method does cut through the toasted grease, but we have to put in a bit more effort to get rid of all the specks. It also made a mess in the oven.