Webpart list property using PNPJS

This is what I am left with for now. My this.lists object is still empty before it gets to the PropertyPaneDropdown object and I don't know what to do to fix that.

  protected fetchOptions(): IPropertyPaneDropdownOption[] {
    var options: Array<IPropertyPaneDropdownOption> = new Array<IPropertyPaneDropdownOption>();
    sp.web.lists.select('ID', 'Title', 'DefaultViewUrl').orderBy('Title').get().then(function(data){
      for (let i = 0; i < data.length; i++) {
        options.push({
          key: data[i].Title,
          text: data[i].Title
        })
      }
      return options;
    });
    return null;
  }

  protected getPropertyPaneConfiguration(): IPropertyPaneConfiguration {

    if (!this.lists) {
      this.lists = this.fetchOptions();
      this.onDispose();
    }

    return {
      pages: [
        {
          header: {
            description: this.description
          },
          groups: [
            {
              groupName: 'Properties',
              groupFields: [
                PropertyPaneDropdown('list', {
                  label: 'List',
                  options: this.lists
                })
              ]
            }
          ]
        }
      ]
    };
  }